Many patients suffer from orthopedic injuries or bone degenerative conditions that arise during exercise or over time during normal wear and tear. In some cases, the patient's bone becomes warped or has growths or other lesions that arise from extensive use of the bone. Athletes, in particular, may experience that condition when doing heavy workouts, especially in the area of the femoral connection to the acetabulum. In femoroacetabular impingements, an area around the femoral head or the acetabular rim bulges with excess bone growth to the point where the femoral head is impinged when moving about the acetabulum, a condition that is often very painful. A cam impingement results when an abnormality on the surface of the femoral head or neck contacts the rim of the acetabular socket. A pincer impingement results when a patient's acetabulum is deeper than is normal, and the deep socket restricts full movement of the femoral head.
Orthopedic surgeries are performed to resurface bones, such as knees, hips, shoulders, ankles, and elbows that are impinged or otherwise damaged by stress and wear or injury. In hip and femoral resurfacing procedures, treatment approaches may involve milling or burring the femoral head to relieve impingement. The milling and burring is often done by free-hand, based on visual estimates of the location, depth and dimension of the bone. The size and fit between the resurfaced bone and the acetabulum or other joint can vary—in some cases being too loose, and in others too tight. Similarly, in surgeries that involve shaping a bone to receive an implant, free-hand cutting may be too imprecise leaving the bone location too large or small to properly seat the implant.
Computer assisted methods have been developed that provide graphical images of bones and use software that allows the surgeon to cut the bone and install an implant to fit a surgical site more precisely. During a computer-assisted surgery (CAS), a surgeon uses a visual image of the patient's anatomical site to create an implant that fits the site or to alter the site to receive an implant. Example CAS systems are found in U.S. application Ser. No. 12/240,992 and U.S. application Ser. No. 12/120,547. In some cases, the physician uses a cutter or other surgical tool to resect the bone. In most systems, the surgical tool is guided by a computer assisted system which requires a complex tool registration system that can be difficult to use and expensive. Improved methods and systems are needed for resurfacing bone regions particularly in patients with femoroacetabular impingements and other bone conditions.